DE3382781T2 - Oil and fuel compositions, use of polymers as additives in them and methods of making the polymers. - Google Patents

Abstract

Substantially or fully hydrogenated (C6 or lower) diolefin-lower (C1-C8) alkyl acrylate or methacrylate copolymers can be used as additives to improve the viscosity index (VI) of lubricating oils. The preferred copolymer is a fully hydrogenated, high molecular weight copolymer of 1,3-butadiene and methyl methacrylate containing at least 71 mole percent 1,3-butadiene. A pour point depressant, VI improving polymer additive for lubricating oils is provided by incorporating a higher (C12-C20) alkyl methacrylate in the copolymer. A dispersant VI improving copolymer for lubricating oils and a dispersant for hydrocarbon fuels may be prepared by graft polymerizing a polar, nitrogen-containing graft monomer onto these copolymers.

Description

This invention relates to oil and fuel compositions, polymers useful as additives therein, and processes for making the polymers.

More particularly, this invention relates to a hydrogenated copolymer of a diolefin and a lower alkyl methacrylate or lower alkyl acrylate, preferably of high molecular weight, wherein the hydrogenated copolymer is graft polymerized with a polar, nitrogen-containing graft monomer to provide a dispersant, VI improving additive for lubricating oils and a dispersant for hydrogen fuels. Incorporation of a higher alkyl methacrylate into the monomer charge of the copolymer provides a pour point depressant VI improver for lubricating oils.

A variety of additives have been proposed to impart favorable properties to lubricating oils and hydrocarbon fuels. These properties include improved viscosity, improved viscosity/temperature relationships, dispersibility, pour point depression, oxidation inhibition, anti-rust and anti-wear properties. The ability of a lubricant to provide adequate flow at low temperatures and good film thickness at high temperatures is referred to as good viscosity/temperature relationship. Dispersibility refers to the ability of a lubricant to prevent settling of sludge and deposits formed by direct oxidative degradation of the lubricant or as a result of complex reactions between gasoline and exhaust gases in automobile crankcases. If these deposits are not dispersed in the lubricating oil, they settle and cause clogging of filters and possible seizure of moving parts where tight clearances are involved. In addition, dispersants are added to gasoline and middle distillate fuels such as domestic heating oils, diesel fuels and jet fuels because these fuels tend to oxidatively deteriorate when left standing, forming gummy deposits. In the case of gasoline, such gummy residues are deposited in the carburetor, making it impossible to control the air/fuel ratio.

The main types of conventional lubricating oil additives include polymethacrylates and copolymers of polymethacrylates, olefin copolymers and hydrogenated diene/styrene polymers.

Polymethacrylates exhibit excellent viscosity/temperature relationships in lubricating oils as a result of their differential solubility in the lubricating oil at high and low temperatures. Polymethacrylate additives can be modified by graft polymerizing polar, nitrogen-containing monomers onto the polymethacrylate backbone to impart dispersibility.

Olefin copolymers, such as ethylene/propylene copolymers, are more effective lubricating oil thickeners than polymethacrylates. The improved thickening efficiency allows them to be effective at lower concentrations in the lubricating oil than polymethacrylates. The improved thickening efficiency of olefin copolymers is a function of the high percentage of their molecular weight in the polymer backbone, compared to polymethacrylates, which have a lower percentage of their molecular weight in the backbone and a higher percentage of their molecular weight in the side chain alkyl groups. Olefin copolymers can also be modified by a different graft polymerization process than that used to graft polymerize polymethacrylates to introduce dispersing functionality onto the olefin copolymer backbone. While olefin copolymers are excellent thickeners, they do not possess the excellent viscosity/temperature relationships of polymethacrylates. In addition, olefin copolymers do not exhibit pour point depressants, and the addition of sufficient amounts of conventional pour point depressant additives to the olefin copolymer can result in an incompatible lubricating oil concentrate.

Hydrogenated diene/styrene copolymer additives, such as those disclosed in US-A-4181618, are also effective lubricating oil thickeners, but are less oxidatively stable than polymethacrylates and do not possess the excellent viscosity/temperature relationships of polymethacrylates.

Accordingly, it would of course be advantageous to combine the beneficial properties of polymethacrylates with the beneficial properties of olefin copolymers to create a lubricating oil additive that has the best characteristics of each type of additive. However, physical blends of polyolefins and polymethacrylates are incompatible. Blends containing more than about 5% by weight of polyolefin separate into two phases in the lubricating oil, and this incompatibility renders a simple physical combination ineffective as an oil additive in most cases.

German Offenlegungsschrift 2,905,954 is directed to a phase stabilizer or emulsifier composition which compatibilizes polymethacrylates and olefin copolymers in lubricating oil. The graft and block emulsifier compositions have sequences which are compatible with the olefin copolymer and other sequences which are compatible with polymethacrylates. The emulsifier composition must be present at levels above 5% by weight to compatibilize polymethacrylates and olefin copolymers. However, these compatibilized blends must be used at concentrations of about 2.0% to impart an effective viscosity index to lubricating oils. In addition to the need for such high concentrations, the limit pumping temperature of lubricating oils containing an effective amount of a compatibilized polymethacrylate/olefin copolymer is not as low as can be achieved with the copolymers of the present invention.

US Patent 3,621,004 relates to lubricating oil compositions containing polymeric compounds with viscosity-improving properties and with dispersant properties. These polymeric compounds are prepared by copolymerizing one or more olefins containing two to six carbon atoms per molecule, with one or more alkyl esters of unsaturated carboxylic acids, preferably containing eight or more carbon atoms per molecule, for example lauryl methacrylate, and one or more esters of unsaturated carboxylic acids in which the part of the molecule derived from the alcohol contains at least one free hydroxyl group, such as beta-hydroxyethyl methacrylate. A programmed copolymerization or a low conversion copolymerization is necessary to ensure that the ratio between the concentration of the monomers in the mixture to be polymerized remains constant during the polymerization. The copolymer is then reacted with cyclic ethers, for example ethylene oxide, to form the lubricant additive.

British Patent No. 1,112,749 also discloses polymeric VI improvers and/or thickeners for a lubricating oil. These additives are formed by copolymerizing one or more mono or diolefins having six carbon atoms per molecule or less with either one or more alkyl esters of unsaturated monobasic carboxylic acids, in which the alkyl group of at least one ester preferably contains eight or more carbon atoms, or with one or more alkyl esters of unsaturated polybasic carboxylic acids. Specific molar ratios of the monomers are required to minimize the undesirable formation of homopolymers of the esters or olefins. The preferred additive is a copolymer of ethylene or butadiene and lauryl methacrylate or di(2-ethylhexyl) itaconate.

British Patent '749 and U.S. Patent No. 3,621,004 do not disclose that copolymers of only ethylene and methyl methacrylate can be effective as lubricating oil additives. This is because it would be expected that as the number of carbon atoms in the alkyl group of the methacrylate component decreases, the solubility of the resulting copolymer in the lubricating oil would decrease. There are no reported attempts to successfully form copolymers of olefins and methyl methacrylate or lower alkyl acrylates which are effective as lubricating oil additives. British Patent '749 also discloses partially hydrogenated copolymers of butadiene and lauryl methacrylate; however, the VI improvement achieved with such an additive is less than satisfactory at high temperatures.

French Patent No. 2,273,057 discloses hydrogenated butadiene/methyl methacrylate copolymers having a low number average molecular weight (less than 10,000). These copolymers are disclosed to be useful as flow improvers for hydrocarbon fluids. However, they are not disclosed to be useful as VI-improving additives for high and low temperature lubricating oils. Their function is to modify the crystallinity of alkanes in hydrocarbon fluids at low temperatures.

German Offenlegungsschrift 2,322,079 discloses block polymer additives for lubricating oils. These additives are copolymers of hydrogenated blocks of conjugated dienes, such as polybutadiene or polyisoprene, and optionally hydrogenated blocks of at least one monoalkenylpyridine, acrylate, methacrylate, acrylonitrile and alpha-olefin oxide. The copolymer preferably contains 10 to 99 percent by weight and more, preferably 40 to 97 percent by weight, of the hydrogenated blocks of conjugated Dienes. These sequential anionically polymerized block copolymers are structurally different and are prepared by a different process than the random copolymers of the present invention. Because the block copolymers comprise sequences of homopolymers coupled together, one would expect that these homopolymers could associate with each other to form aggregates and that this would result in different solubility properties than the copolymers of the present invention.

Yokota and Hirabayashi in Macromolecules, Vol. 14 No. 6, 1981, pages 1613-16, "Synthesis of a Sequence-Ordered Copolymer: Hydrogenation of Alternating Butadiene/Methyl Methacrylate Copolymer" disclose synthesizing perfectly alternating copolymers of butadiene and methyl methacrylate and a process for hydrogenating such copolymers. These hydrogenated alternating copolymers would not be expected to be soluble in lubricating oils below about 50°C, as a result of very high polarity and possibly from crystallinity resulting from the regular nature of the copolymer. Accordingly, these copolymers would not be expected to be effective VI-improving additives.

Hydrogenated butadiene/methyl methacrylate copolymers would be expected to be very similar to ethylene/methyl methacrylate copolymers. We have found that ethylene/methyl methacrylate copolymers prepared by emulsion polymerization at high pressures greater than 7.91 bar (100 psig) are too insoluble in lubricating oils to be useful as VI improvers. The insolubility of ethylene/methyl methacrylate copolymers in oil is probably the result of crystallization of ethylene blocks. These blocks tend to occur because of the significantly differing reactivities of ethylene and methacrylate esters. We have also found that high molecular weight hydrogenated polybutadiene prepared by emulsion polymerization techniques and low molecular weight hydrogenated polybutadiene prepared by free radical polymerization techniques are also too insoluble in oil to be effective additives. The partial insolubility of hydrogenated polybutadiene is also probably due to polyethylene-type crystallinity. In addition, high molecular weight polymethacrylate is extremely polar and practically insoluble in lubricating oils which have low polarity.

We have now unexpectedly found that catalytically hydrogenated high molecular weight copolymers of conjugated diolefins having six carbon atoms or less per molecule and alkyl acrylates or alkyl methacrylates and mixtures thereof where the alkyl group of the acrylate or methacrylate contains eight carbon atoms or less per molecule are soluble in lubricating oil and can provide an effective VI improving additive for lubricating oils.

It is an object of this invention to provide a new VI improving copolymer additive for lubricating oils which has the desirable properties of a conventional polymethacrylate and olefin copolymer oil additives

It is a further object of this invention to graft polymerize a polar nitrogen-containing graft monomer onto the backbone of a hydrogenated diolefin/lower alkyl acrylate or -/lower alkyl methacrylate copolymer to provide a dispersant VI improver for a lubricating oil and for hydrocarbon fuels.

According to one aspect of the invention there is provided a graft copolymer characterized by comprising: a copolymer substrate and a polar nitrogen-containing graft monomer polymerized onto the substrate, and wherein the copolymer substrate: (I) comprises the polymerized product of (a) a conjugated diolefin having 6 carbon atoms or less per molecule and (b) a lower alkyl acrylate or lower alkyl methacrylate in which the alkyl group contains 8 carbon atoms or less per molecule; (II) has a weight average molecular weight of from 60,000 to 1.6 x 106; and (III) is hydrogenated to have no more than 5% residual unsaturation as determined by spectroscopy.

According to a second aspect, the invention provides a process for producing a hydrogenated copolymer characterized by comprising: (I) emulsion copolymerizing (a) a conjugated diolefin having 6 carbon atoms or less per molecule with (b) a lower alkyl acrylate or lower alkyl methacrylate in which the alkyl group contains 8 carbon atoms or less per molecule, optionally together with (c) one or more higher alkyl methacrylates in which the alkyl groups contain 12 to 20 carbon atoms, in an aqueous surfactant solution in the presence of a catalyst at a polymerization temperature of 5 to 40°C to form a copolymer; (II) and catalytically hydrogenating the copolymer in the presence of a hydrogenation catalyst at a pressure of 7.91 bar to 35.09 bar (100 to 500 psig) to reduce substantially any diolefin unsaturation of the copolymer so that there is no more than 5% residual unsaturation as determined by spectroscopy; (III) if necessary, degrading the copolymer before or after the hydrogenation step (II) so that the copolymer has a weight average molecular weight of 60,000 to 1.6 x 106; and (IV) graft polymerizing the polar nitrogen-containing monomer onto the hydrogenated copolymer.

A third aspect of the invention includes an oil composition comprising (i) a lubricating oil and (ii) a dispersing and viscosity index improving amount of a graft copolymer according to the invention.

A fourth aspect of the invention provides an oil composition comprising: (i) a lubricating oil and (ii) a dispersing, pour point depressing and viscosity improving amount of a graft copolymer according to the invention, in which graft copolymer the copolymer substrate comprises the polymerized product of (a) a conjugated diolefin having 6 carbon atoms or less per molecule, (b) a lower alkyl acrylate or lower alkyl methacrylate in which the alkyl group contains 8 carbon atoms or less per molecule, and (c) one or more higher alkyl methacrylates in which the alkyl group contains 12 to 20 carbon atoms.

A fifth aspect of the invention provides a fuel composition comprising (i) a hydrocarbon fuel and (ii) a dispersing amount of a copolymer of the invention.

The term substantially hydrogenated as used herein means that the copolymers are hydrogenated to an extent that up to 5% residual unsaturation is present as determined by spectroscopy.

The high molecular weight hydrogenated graft copolymers of this invention are useful as dispersant VI improvers for lubricating oils and can be modified to produce multifunctional pour point depressant and dispersant VI improvers.

These VI improvers are hydrogenated copolymers of conjugated diolefins, which have six carbon atoms or less per molecule, and lower alkyl acrylates or lower alkyl methacrylates, where the alkyl group contains eight carbon atoms or less per molecule.

Suitable conjugated diolefin monomers useful in this invention include 1,3-butadiene, cis- and trans-1-methyl-1,3-butadiene (piperylene), 2,3-dimethyl-1,3-butadiene and 2-methyl-1,3-butadiene (isoprene). The preferred conjugated diolefin monomer is 1,3-butadiene.

Suitable lower alkyl acrylate and lower alkyl methacrylate comonomers include methyl, ethyl, butyl, propyl, isopropyl, sec-butyl, isobutyl, tert-butyl acrylate or methacrylate and mixtures thereof. The preferred lower alkyl acrylate or methacrylate is methyl methacrylate.

The copolymer substrates used in this invention can be prepared by any standard polymerization technique capable of forming a copolymer of a diolefin and a lower alkyl acrylate or methacrylate having a sufficiently high molecular weight. Emulsion polymerization has been found to be the preferred method for preparing random copolymers of a diolefin and a lower alkyl acrylate or methacrylate having a sufficiently high molecular weight. Emulsion polymerization preferably comprises preparing a first aqueous surfactant mixture of deionized water, an anionic surfactant, for example sodium lauryl sulfate, and a reducing portion of a redox initiator system, for example tetrasodium pyrophosphate and ferrous sulfate heptahydrate. The monomers and the oxidation part of the redox initiator system, for example cumene hydroperoxide, tert-butyl hydroperoxide or diisopropylbenzene hydroperoxide, are added to the first aqueous surfactant mixture under a nitrogen atmosphere. Chain transfer agents can also be added to the monomer mixture. Polymerization initiators which generate free radicals and are different from the redox systems described above can also be used in the emulsion polymerization process. These initiators are, for example, azo initiators such as azobisisobutyronitrile and 2,2'-azobis(2,4dimethyl-4-methoxy)valeronitrile, manufactured under the trademark Vazo 33 by E.I. duPont, and water-soluble persulfate initiators such as sodium persulfate and ammonium persulfate, optionally with reducing agents. Whatever initiator system is chosen, it is important that the system generates free radicals at an appropriate rate at the temperature chosen for the polymerization reaction.

Further steps in the process may be as described below.

The ratio of the monomer mixture in the feed preferably approximates the desired ratio of polyolefin to polyacrylate or polymethacrylate units in the final copolymer. The emulsion reaction mixture is maintained at a polymerization temperature of -10°C to 60°C, preferably 5°C to 40°C, and more preferably 20°C to 30°C. Once polymerization has begun, additional monomers are slowly added to the reaction mixture at a constant rate. At the same time, a second aqueous surfactant mixture containing a nonionic surfactant such as Triton X-405 or Triton N-100 ("Triton" is a trademark of Union Carbide) and an additional anionic surfactant are gradually added to the reaction mixture to form a suitable emulsifying environment for copolymerization. The reaction is allowed to proceed to a high conversion of the order of about 50-90%, and preferably 70-90%, of the completed reaction. The emulsion copolymer is either precipitated from the solution, as by methanol-containing hydroquinone, or isolated from the mixture, e.g. by extraction and azotropic distillation. The precipitated emulsion copolymer is then washed and dried.

Methyl methacrylate is preferred as a lower alkyl methacrylate comonomer for emulsion copolymerization with the conjugated diolefin monomers. Methyl methacrylate is partially soluble in water and has a favorable reactivity ratio to the conjugated diolefins. This favorable reactivity ratio allows the formation of copolymers with a substantially uniform composition compared to the monomer feed.

The conditions used for emulsion polymerization, and particularly the temperature of emulsion polymerization, have an important effect on the manner in which the conjugated diolefin monomer polymerizes. In turn, the manner in which the conjugated diolefin monomer polymerizes has an effect on the solubility of the resulting copolymer in a lubricating oil. It is claimed that when 1,3-butadiene polymerizes, the polybutadiene formed has a microstructure. A microstructure is a term used to distinguish star chemistry and the arrangement of monomer units from macrostructure. The microstructure of polybutadiene includes cis-1,4-polybutadiene, trans-1,4-polybutadiene and vinyl-1,2-polybutadiene. Based on the literature (JL Binder, Ind. Eng. Chem. 46 1727 (1954), "Microstructure of Polybutadiene and Butadiene Styrene Copolymers" the microstructure of polybutadiene can be estimated at different emulsion polymerization temperatures. At an emulsion polymerization temperature of -5ºC the polybutadiene microstructure contains about 13% cis, 75% trans and 12% vinyl. At an emulsion polymerization temperature of about 50ºC the polybutadiene microstructure contains about 18% cis, 65% trans and 17% vinyl. Increasing the emulsion polymerization temperature favors the formation of vinylpolybutadiene and cis-polybutadiene at the expense of the formation of trans-polybutadiene. Increasing the amount of vinylpolybutadiene contained in the microstructure or incorporated in the chain is desirable when producing a copolymer that must be soluble in a lubricating oil. Increasing the vinylpolybutadiene Chain formation in the microstructure increases the ethyl branches in the polymer, thereby reducing the occurrence of molecular interactions, melting point and the possibility of polyethylene-type crystallinity, which in turn reduces the possibility of decreasing the solubility of the copolymer additive in a lubricating oil. However, increasing the polymerization temperature above 40°C reduces the amount of possible monomer conversion without introducing too much crosslinking. Accordingly, we have found that the preferred temperature range for emulsion polymerization is 5°C to 40°C to form copolymers which, upon hydrogenation, are effective VI improvers for lubricating oils.

We have also found that the ratio of the concentration of the conjugated diolefin monomer to the concentration of the lower alkyl acrylate or lower alkyl methacrylate monomer in the monomer feed can be important in minimizing polyethylene-type crystallization without introducing excessive polyacrylate or polymethacrylate polarity. Hydrogenated copolymers containing a molar ratio of polybutadiene to polyacrylate or polymethacrylate of about 2:1 or less than about 2.5:1 may not be effective as commercial VI improvers for lubricating oils. Although these copolymers can improve the viscosity index of a lubricating oil, the copolymers tend to settle out of solution upon storage. This storage instability may be a function of polymethyl methacrylate polarity or polyethylene-type crystallinity. Hydrogenated copolymers of methyl methacrylate and at least 71 mole percent and less than 100%, and preferably less than 98%, hydrogenated 1,3-butadiene can be lubricating oil soluble, storage stable, and effective VI improvers for lubricating oils at low application levels.

If the number of carbon atoms per molecule in the alkyl group of the lower alkyl acrylate or lower alkyl methacrylate monomer is increased, the required concentration of the diolefin monomer in the monomer feed can be reduced to below 71 mole percent without adversely affecting the solubility and storage stability of the hydrogenated copolymer in a lubricating oil. However, reducing the diolefin monomer concentration to below 71 mole percent reduces the effectiveness of the copolymer as a VI improver. If the diolefin content in the monomer feed is reduced to slightly less than 71 mole percent, a mixture of low carbon alkyl acrylate and methacrylate monomers where the alkyl group contains eight or fewer carbon atoms per molecule, such as methyl acrylate and methyl methacrylate, can be used to produce a hydrogenated copolymer which is soluble, storage stable and which is effective as a VI improver.

The molecular weight of the copolymers prior to hydrogenation can vary within a wide range of molecular weights, for example from about 100,000 to about 10,000,000 weight average molecular weight and from about 10,000 to about 5,000,000 number average molecular weight. The molecular weight of the copolymer can preferably be controlled by the inclusion of various chain transfer agents having a hydrogen sulfide bond, such as n-dodecyl mercaptan, t-dodecyl mercaptan, t-butyl mercaptan, n-hexyl mercaptan and the like, wherein the monomer mixture is present during the copolymerization process in concentrations of from about 0.1% to about 0.4% by weight of total monomers. Less active chain transfer agents such as p-diisopropylbenzene, toluene and N-oil 100 may also be used in concentrations of from about 5 to 10%. N-oil refers to a neutral oil containing no additives and prepared by vacuum frictional treatment of a crude petroleum distillate with a cut at 375-550ºC followed by decolorization and dewaxing. The prefix, i.e. 100 or 150, refers to the Saybolt viscosity (Saybolt Universal Seconds [SUS]) at a specified temperature, i.e. 37.8ºC (100ºF) or 65.6ºC (150ºF), respectively.

When the concentration of diolefin monomer in the monomer mixture to be polymerized exceeds 71 mole percent, composition drift, that is the difference between the composition of the monomer mixture and the composition of the resulting copolymer, is not significant. The composition of the resulting copolymer can closely approximate the composition of the monomer mixture. The lack of significant composition drift allows the copolymerization to proceed to high conversions, on the order of 70-90% of the total conversion, without the need to vary the composition of the monomer mixture added during copolymerization (variable feed addition) or programmed copolymerization to low conversion as taught in the prior art. While complete conversion is possible without variable feed addition, this is not desirable because significant crosslinking of the copolymer can occur near complete conversion. Significant crosslinking of the high molecular weight copolymer is undesirable because it makes subsequent handling of the copolymer extremely difficult. Moderate crosslinking of the high molecular weight copolymer, as determined by a reciprocal swelling volume of less than about 0.01 to 0.05 in solvent, can be tolerated because such moderate crosslinking does not result in a copolymer that cannot be handled after filtration to remove the crosslinked polymer or to a lower molecular weight after subsequent degradation. However, it is desirable to maximize the extent of copolymerization while minimizing crosslinking to form a substantially soluble copolymer.

The high molecular weight copolymer substrates used in this invention can be catalytically hydrogenated to form a hydrogenated VI improving copolymer. The copolymer can be transferred by extraction directly from an aqueous emulsion into a hydrogenation solvent if the copolymer was prepared by an emulsion polymerization process. Alternatively, the copolymer can be precipitated from the emulsion and dried before being redissolved in the hydrogenation solvent. Combinations of extraction and precipitation can also be used to isolate the copolymer and transfer it to the hydrogenation solvent. The hydrogenation solvent is any inert aromatic or saturated hydrogen solvent in which the copolymer can dissolve, such as toluene, cyclohexane, benzene, xylene, methylcyclohexane, tetralin, decalin, t-butylbenzene, dimethylcyclohexane, ethylbenzene and the like. A material capable of donating hydrogen, such as hydrogen gas or cyclohexene, tetralin, limonene, vinylcyclohexene and the like, and a catalyst are added to the copolymer solution in a reactor under a nitrogen atmosphere at about 25-40°C. Hydrogen is the preferred material for donating hydrogen. When hydrogen gas is used, the preferred hydrogenation catalyst is a solution of an anhydrous nickel, iron or cobalt salt, such as nickel di(2-ethylhexanoate), an anion of pentanedione, nickel di(2-ethylhexanoate), nickel (cyclohexanebutyrate) or nickel di(naphthenate) and the like. Nickel di(acetylacetonate) and triethylaluminum, a reducing agent, in toluene is the preferred hydrogenation catalyst system when hydrogen gas is used. Other reducing agents which can be used with the hydrogenation catalysts include triisobutylaluminum, n-butyllithium and trimethylaluminum. When a hydrogen donor material other than hydrogen gas is used, a catalyst containing about 10 wt.% of a Group VIII metal such as palladium, platinum, nickel and the like on a carbon substrate can be used as the hydrogenation catalyst.

The reactor containing the polymer, hydrogen donor material and catalyst solution is pressurized to about 2.05 bar to about 69.96 bar (about 15 psig to 1000 psig), preferably 7.91 bar to 28.59 bar (100 psig to 400 psig). The reactants and catalyst are stirred and heated to between 40°C and 120°C. The temperature of the reaction mixture will increase by about 10-30° as a result of the exothermic nature of the hydrogenation reaction. The hydrogenation reaction is complete when less than 5% unsaturation and preferably less than 2% unsaturation remains as determined by NMR and/or IR spectra. The substantially fully hydrogenated copolymer is freed of catalyst residues by washing with an acid, for example citric or hydrochloric acid. The polymer is then stripped of solvents and volatiles (quick distilled) and the polymer is formulated by addition to neutral oil, preferably to provide an oil composition in the form of a solution of the hydrogenated VI-improving copolymer in oil. A solid 100% hydrogenated copolymer can also be prepared and added directly to a lubricating oil; however, a concentrate in N-oil is the usual way of providing the polymer because of its ease of handling and its rapid dissolving in a lubricating oil.

When polymeric VI improvers are subjected to severe mechanical stresses from operating equipment, the polymer may degrade, reducing the beneficial effect such additives have on the viscosity/temperature properties of a lubricant. Polymers that are resistant to this tendency to mechanically degrade in service are said to have good shear stability. The ability of a VI improver to resist mechanical degradation in use depends on a number of factors, one of which is molecular weight. A very high molecular weight polymer, although initially exerting highly effective control over viscosity/temperature properties, will degrade excessively in service and thus lose much or even all of its effectiveness.

The hydrogenated, non-predegraded copolymer substrates used in the present invention may also have a high molecular weight to be useful, even though they are good VI improvers, i.e., they have poor shear stability. Means of bringing the molecular weight down to a convenient range where shear stability is good are readily available. Only mechanical or sonic degradation of the product is required to adjust the molecular weight to the preferred molecular weight.

The copolymer can be degraded by mechanical degradation or by sonic degradation to improve its shear stability by reducing its molecular weight to the desired range of about 60,000 to about 1.6 x 106 weight average molecular weight and about 20,000 to about 400,000 number average molecular weight either before or after hydrogenation. The preferred weight average molecular weight is 80,000 to one million.

Any means of degradation is acceptable, such as in a gear pump or extruder, but homogenization is preferred. In a homogenization process, the polymer is forced under very high pressure through a device that uses variously designed throttle valves and narrow orifices. Such a device can produce shear rates of 5,000 sec-1 and more, preferably about 10,000 and about 1,000,000 sec-1. Commercial devices such as those manufactured by Manton-Gaulin Manufacturing Company or modifications thereof can be used. Such equipment can be operated at pressures up to about 1,379 bar (about 20,000 psi) to produce the necessary shear stress. The homogenization process can be applied either batchwise or continuously, depending on the extent of degradation desired.

The shear stability of a VI improver is determined using a sonic shear test (ÄSTM D-2603). The shear stability measurement used here is the percent shear loss in the viscosity of the oil attributable to the polymer, abbreviated as % SLDTP. The lower the % SLDTP, the more stable and resistant the additive is to shear degradation.

The VI of a lubricating oil is a measure of the rate of viscosity change of a lubricating oil with temperature. The higher the VI, the less tendency the viscosity of the oil will change as a function of temperature. The VI or VIe is determined from the viscosities of the oil at 37.8ºC (100ºF) and 98.9ºC (2 10ºF) according to ASTM test D567 or D2270. The D2270 test is used to determine a VI above 100 and these VIs are reported as VIe.

The improvement in viscosity achieved with a polymer additive must also be evaluated in conjunction with the amount of polymer added to the lubricating oil to achieve the desired VI improvement. The higher the viscosity index achieved at the lowest percentage of polymer added to the lubricating oil, the more effective the polymer additive is as a VI improver.

The viscosity of a lubricating oil at low temperature is also important in determining the effectiveness of a VI improver. The viscosity of a lubricating oil at low temperature is by its pumping limit temperature (BPT). This BPT is the lowest temperature at which the lubricating oil containing the VI improver can be pumped vertically from the oil sump beneath the engine to the valve level and other parts requiring lubrication. The BPT is measured using a mini-rotary viscometer test (ASTM D-3829) and forms part of the classification of SAE Viscosity Grades for Engine Oils of SAE J-300, Sept. 80.

Oil compositions according to the invention preferably have a limit pumping temperature of less than -30°C and may be stable to mechanical shear degradation and thermal degradation.

We have found that the hydrogenated copolymer substrates used in this invention provide useful VI improvement in lubricating oils at low use levels while providing low BPTs and low % SLDPT. In fact, comparative testing with conventional lubricating oil additives has shown that the hydrogenated copolymers provide a blending advantage of 35-45% (low use levels) over conventional polymethacrylate VI improvers with comparable VI, % SLDPT and BPT. In addition, the hydrogenated copolymers have better shear stability (% SLDPT) and better low temperature viscosity (BPT) than conventional ethylene/propylene copolymer VI improvers at lower use levels in lubricating oils than are used with ethylene/propylene copolymers. In addition, the hydrogenated copolymers may also exhibit improved thermal or oxidative stability over known VI improvers, as determined by a standard thermo-gravimetric analysis technique, in air or nitrogen.

The copolymer substrates used in this invention can be modified to form multifunctional pour point depressants and dispersant VI improvers for lubricating oils and dispersants for hydrocarbon fuels. Pour point is the lowest temperature (°F) at which an oil will flow (ASTM D-97) and is an important parameter in cold start-up. A pour point depressant lowers the pour point of a lubricating oil so that it will pour at a lower temperature. The copolymer substrates can be modified to provide pour point depressability by incorporating higher alkyl (C12-C20) methacrylates and mixtures thereof, for example in an amount of from 5 to about 100 mole percent based on the percentage of total methacrylates, into the monomer mixture of the polymerization feed. The preferred higher alkyl methacrylates used to impart stock reduction capability to the copolymers of this invention include mixtures of C16-C20 (cetyl, stearyl and eicosyl) methacrylates, C12-C15 (dodecyl, tridecyl, tetradecyl, pentadecyl) methacrylates and mixtures thereof. Mixtures of high carbon number alcohols derived from natural sources may also be used.

The copolymerization technique and hydrogenation process used to prepare these pour point depressant VI improvers may be substantially identical to that used to prepare the hydrogenated diolefin/lower alkyl acrylate or lower alkyl methacrylate VI improver copolymers. Hydrogenation of a pour point depressant copolymer requires however, the use of about 1.5 to about 2 times the amount of catalyst required to hydrogenate single function VI copolymers. The resulting hydrogenated pour point depressant VI improver copolymers can contain up to about 5% unsaturation without adversely affecting the solubility and thermal and oxidative stability of the copolymer in the lubricating oil. The hydrogenated pour point depressant VI improvers can have high viscosity indices (VIes) but can be slightly less shear stable (% SLDPT) than the non-pour point depressant VI improver copolymers. The application levels required to achieve high VIe are significantly lower than the levels required for polymethacrylates and are comparable to or slightly higher than the application levels required for conventional ethylene/propylene copolymer additives. The pour point of a base oil can be significantly reduced by at least 2.78ºC (5ºF) and up to about 19.44ºC (35ºF) by adding various amounts of the pour point depressant, VI-improving copolymer to the oil.

The VI-improving copolymer substrates are modified to incorporate dispersibility. The dispersing VI-improving copolymers and the dispersing pour point depressing VI improvers of the present invention are preferably prepared by a conventional free radical initiated graft polymerization process of a polar nitrogen-containing graft monomer, for example N-vinylpyrrolidone and 2- or 4-vinylpyridine, onto the hydrogenated copolymer backbone or substrate. Other possible graft monomers include N,N-dimethylaminoethyl acrylate or methacrylate, 2-methyl-5-vinylpyridine, vinylimidazole and t-butylaminoethyl acrylate or methacrylate.

A preferred graft polymerization process is described below.

The copolymer is dissolved in a suitable inert solvent such as pale neutral oil or the higher alkyl isobutyrates derived from the hydrogenation of higher alkyl methacrylates, at a polymer concentration of about 15 to about 80 weight percent. Other solvents for the grafting reaction include chlorinated aromatics such as chlorobenzene, o-dichlorobenzene, 1,2,4-trichlorobenzene or alpha-chloronaphthalene, t-butylbenzene, white polymerization oil, cyclohexane and the like. It may also be possible to carry out the graft polymerization in the absence of solvent and using intimate, high intensity mixing such as in a Banbury mixer, Sigma paddle mixer or an extruder, which are conventionally used to mix rubbers. The resulting graft copolymers were obtained with a very high solids content in the order of about 80%.

The polymer solution is then stirred and heated to about 110°C. The graft monomer is then mixed into the polymer solution. The concentration of the graft monomer is about 2 to about 10 weight percent of the hydrogenated copolymer. A free radical initiator having a decomposition temperature higher than the temperature of the polymer solution is then added to the polymer and the graft monomer solution. The concentration of the free radical initiator is about 0.5 to about 2 weight percent of the hydrogenated copolymer. The solution of hydrogenated copolymer, solvent, graft monomer and free radical nitiator is intimately mixed. Then the reaction temperature is gradually raised to or above the decomposition temperature of the initiator. In the case of a t-butyl perbenzoate initiator, the temperature is raised to about 120-140°. Then the temperature is maintained or further increased to about 140-150°C to complete the graft polymerization reaction. The reaction usually takes about one to two hours. The reaction product will typically contain essentially no gel and about 0.05 to 0.5 weight percent homopolymerized graft monomers in the form of a turbidity, and preferably less than about 0.05 to 0.1 weight percent. Any gel which is formed is removed by filtration or by centrifugation. The final randomly grafted polymer solution contains about 15 to about 60 weight percent solids and from about 0.2 to about 1.0 percent nitrogen (Kjeldahl analysis). The finished graft copolymer can be further diluted in an oil solution to facilitate handling.

The free radical initiator is any free radical source capable of abstracting hydrogen from the hydrogenated copolymer backbone. Examples include alkyl peroxyesters, alkyl peroxides, alkyl hydroperoxides, diacyl peroxides, and the like. While t-butyl perbenzoate is the preferred initiator, other suitable initiators include t-butyl peroctate, di-t-butyl peroxide, t-butyl hydroperoxide, cumene hydroperoxide, benzoyl peroxide, and the like.

While the temperature of the graft polymerization reaction may vary from about 80°C to about 200°C, it is understood that the temperature selected will depend on the decomposition temperature of the initiator as well as the composition of the hydrogenated copolymer substrate and the grafting monomers. Accordingly, it is possible to conduct the grafting reaction at a temperature as low as 25°C or as high as 250°C.

Intimately mixing the substrate copolymer, graft monomers and initiator prior to initiating the graft polymerization reaction and maintaining the temperature below the decomposition temperature of the initiator, at least during addition and mixing of the initiator into the solution, is important to prevent the formation of free radicals until the reactants are fully and intimately mixed. This process eliminates or substantially minimizes the formation of undesirable byproducts, such as a homopolymer, and maximizes grafting of the polar nitrogen-containing monomer to the hydrogenated copolymer substrate.

During the grafting reaction, any solvent medium can be used to prepare the graft copolymer, provided that the medium is substantially inert to the reactants, that is, the medium has little or no chain transfer ability. The preferred solvent is an N-oil 100; however, ortho-dichlorobenzene may be useful in some cases.

The graft copolymers of this invention are also useful as dispersants in fuels. In particular, gasoline and middle distillate fuels such as home heating oils, diesel fuels and jet fuels tend to oxidatively degrade upon standing and form gummy deposits. The graft copolymers of this invention disperse such deposits and thus prevent deterioration of the fuel quality.

The activity of any given polymer as a dispersant can be determined by means of an asphalt dispersibility test. This test determines the ability of the polymer to disperse asphalt in a typical mineral oil. The asphaltenes are obtained by oxidation of a naphthenic oil with air under the influence of a trace iron salt catalyst, such as ferric naphthalenate. The oxidation is conveniently carried out at 175°C for approximately 72 hours by passing a stream of air through a naphthenic oil to form a slurry which can be separated by centrifugation. The slurry is then freed from the oil by extracting it with pentane. It is then taken up with chloroform and the resulting solution is adjusted to a solids content of about 2% by weight by volume.

When a polymer is to be tested for dispersing activity, it is dissolved in a standard oil, such as a solvent extracted 100% neutral oil. Blends can be made to achieve percentages of polymer in oil varying from about 2% to about 0.01% or lower.

A 10 ml sample of a mixture is treated with 2 ml of the standard solution of asphaltenes in chloroform. The sample and reagent are thoroughly mixed in a test tube, and the tube is placed in a forced air oven at either 90ºC or 150ºC for 2 hours to drive off volatile material. The tube is then allowed to cool and the appearance of the sample is noted.

If the polymer has dispersing activity, the oil will appear clear, although colored. Experience has shown that unless a polymer has dispersing activity in the above test, at concentrations below about 2%, it will not improve the cleanliness of engine parts in actual engine tests. If 2% polymer in oil is required to pass the asphalt dispersibility test, the polymer is rated 1P. If 1% polymer in oil is required to pass, the polymer is rated 2P. At 0.5% polymer, the rating is 3P; at 0.25%, the rating is 4P; at 0.12%, the rating is 5P; and at 0.06%, the rating is 6P.

The dispersant pour point depressant graft copolymers of this invention can exhibit high VIes at use level concentrations higher than those required for the hydrogenated VI improvers or the hydrogenated pour point depressant VI improvers, and can also exhibit asphalt dispersibility ratings of 1P to 6P, indicating that they are effective multifunctional dispersant pour point depressant VI improvers for a lubricating oil.

Other additives may be added to the lubricating oil containing the dispersant VI improvers of this invention to provide additional dispersibility, viscosity/temperature control, pour point depressant, high temperature detergency, rust inhibition, antiwear agents, antioxidants, extreme pressure agents, friction modifiers, antifoam agents, or colorants. Accordingly, the following may be used with the products of this invention: polybutene-based succinimides or esters, phosphosulfurized polybutenes, polyacrylates, or polymethacrylates, polyisobutylene, ethylene/propylene copolymers. or terpolymers, hydrogenated styrene/butadiene or styrene/isoprene, N-vinylpyrrolidinone or dimethylaminooctyl methacrylate-containing copolymers with methacrylates, styrene polyesters, ethylene/vinyl acetate copolymers or oligomers, dialkyl fumarate polymers or copolymers, esterified styrene/maleic anhydride copolymers or oligomers, hydrocarbon wax/naphthalate condensate of the Friedel-Crafts type, chlorinated hydrocarbons, alkaline earth metal sulfonates, phenates, alkylates or phenate sulfides, alkaline earth metal alkyl naphthalene sulfonates, zinc or other dialkyl metal dithiophosphates or diaryl metal dithiophosphates, zinc, cadmium, lead, molybdenum or other metal dithiocarbamates, sulfurized or phosphosulfurized esters or Terpenes, hindered phenols, phenothiazine or alkylated phenothiazines, naphthylamines, phenylenediamines, dibenzyl disulfide, sulfurized diisobutylene or triisobutylene, trialkyl or triaryl phosphates, tricresyl phosphate or silicone polymers and the like.

The following examples are presented for illustrative purposes, with all parts and percentages being by weight and temperatures in degrees Celsius unless otherwise specifically stated. The examples illustrate the preparation of hydrogenated copolymers suitable for use as the copolymer substrate in the graft copolymers of the invention, and also illustrate the preparation of graft copolymers of the invention with some of these hydrogenated copolymers.

In the examples (i.e. Tables II to IV) viscosities are given in centistokes (CST), and 1 CST = 1 x 10⁻⁶m²s⁻¹.

example 1 Preparation of a 1,3-butadiene/methyl methacrylate emulsion copolymer

A surfactant solution of 600 mL of deionized water, 0.22 grams of sodium lauryl sulfate, 1.71 grams of tetrasodium pyrophosphate, and 1.79 grams of ferrous sulfate neptahydrate is added to a 2-liter Parr reactor equipped with two propeller-type stirrers on the stirrer shaft and two inlet ports. The reactor is thoroughly purged with nitrogen for 30 minutes while the surfactant solution is stirred. 55 mL of a monomer mixture prepared from 180 grams of methyl methacrylate, 325 grams of 1,3-butadiene, and 1.00 gram of cumene hydroperoxide catalyst is added to the reactor. The temperature of the reactor is maintained between +24ºC and +26ºC. The remainder of the monomer mixture is added to the monomer mixture at a rate of 3.0 mL per minute. At the same time that the remainder of the monomer mixture is added, a second surfactant solution of 14.6 grams of 70% aqueous Triton X405, an ethoxylated t-octylbenzene, and 4.4 grams of sodium lauryl sulfate in 266 grams of deionized water is added to the reactor at a rate of 1.9 ml per minute. The addition of the second surfactant solution takes about 2.5 hours to complete. Agitation and temperature are maintained for an additional 4.5 hours after the monomer mixture is added. Unreacted butadiene is then vented and the emulsion is precipitated into 3 liters of methanol containing 0.2 grams of hydroquinone. The precipitated copolymer is washed with 2 liters of methanol and then with six washes of 3 liter portions of deionized water. The washed, precipitated copolymer is dried in a vacuum for 24 hours at Dried at 35ºC. The finished, dried copolymer weighs 315 grams and contains 77.8 mole percent 1,3-butadiene, determined by NMR.

Examples 2-8 Preparation of a 1,3-butadiene/methyl methacrylate emulsion copolymer in the presence of chain transfer agents

The copolymers of these examples are prepared according to the procedure of Example 1, with various chain transfer agents, such as n-DDM, t-DDM, and N-Oil 100, added to the monomer mixture at a range of weight percent concentrations based on the monomers, to control molecular weight. These chain transfer agents are added to the reactor and are mixed with the monomer feed. The copolymer is isolated according to Example 1 (Examples 5 and 8) by precipitation in methanol or by direct extraction at 70°C into 2 liters of cyclohexane followed by azeotropic distillation to dry the cyclohexane solution and remove methanol (Examples 2-4, 6-7). The extraction typically isolates 50-70% of the copolymer. The remainder can be isolated by precipitation if desired. Complete isolation by extraction is preferred as no redissolution step is required. Polymer yields are measured by evaporating the cyclohexane from a weighed sample.

The properties, the mole percent butadiene concentration and the molecular weight, determined by gel permeation chromatography (GPC), based on a polymethacrylate calibration, are summarized in Table I.

Example 9 Hydrogenation of a 1,3-butadiene/methyl methacrylate emulsion copolymer

The dry copolymer of Example 1 is dissolved in 4 liters of cyclohexane by stirring for 6 hours at 55°C. Hydrogenation of the copolymer is accomplished in a 2-liter Parr reactor in 3 equal portions by adding a catalyst prepared from 1.49 grams of Ni(acac)2 and 7.2 ml of 25% triethylaluminum in toluene to each portion, setting the reactor pressure to 28.59 bar (400 psig) and heating with stirring at 40°C for one hour. Then the temperature is raised to 110°C for about half an hour to about one hour to complete the reaction. The hydrogenated copolymer is freed of catalyst residues by washing twice with 500 mL of 10% aqueous citric acid at 70°C and eight times with 2 liter portions of deionized water. The hydrogenated copolymer is stripped in N-Oil 100, homogenized with four passes at 8000 psig to reduce molecular weight, and pressure filtered through a bed of diatomaceous earth. The IR and NMR spectra of the final homogenized hydrogenated copolymer show no absorptions attributable to double bonds.

Examples 10-16

The copolymers of Examples 2 to 8 are hydrogenated and freed from catalyst residues according to the procedure of Example 9. At the higher mercaptan levels, 2-3 times the amount of catalyst is necessary to achieve complete hydrogenation, as measured by IR and NMR.

The VI and shear stability properties of the hydrogenated copolymers of Examples 9 to 16 in lubricating oil are summarized in Table II.

Example 17 Preparation of a 1,3-butadiene/ethyl acrylate emulsion copolymer

A first aqueous surfactant mixture containing 294.5 grams of deionized water, 1.55 grams of sodium lauryl sulfate, 4.87 grams of Triton X-105 (70% aqueous) (an ethylene oxide adduct of t-octylphenol in which the diameter of ethylene oxide units is about 40), 0.60 grams of ferrous sulfate heptahydrate, and 0.57 grams of tetrasodium pyrophosphate is added to a 1 liter three-neck flask equipped with a dry ice condenser, a paddle stirrer, a dropping funnel, and a nitrogen inlet port. The mixture is stirred to form a homogeneous solution. The flask is purged with nitrogen while the solution is cooled to 5°C with ice water. A monomer mixture is prepared from 60.0 grams of ethyl acrylate, 112.0 grams of 1,3-butadiene and 0.34 grams of n-dodecyl mercaptan (0.2 weight percent based on monomers) and 0.34 grams of cumene hydroperoxide (0.2 weight percent based on monomers). When the aqueous solution reaches 5ºC, 20 ml of the monomer mixture is added to the flask and the reactants are vigorously stirred. Once the first 20 ml of the monomer mixture emulsifies, the remainder of the monomer mixture is added dropwise to the flask over one hour. The temperature of the flask reactants is maintained between 3 and 7ºC by cooling with ice water. At the end of seven and one-half hours, the copolymer is isolated by precipitation in 2 liters of methanol containing 0.2 grams of hydroquinone. The precipitated copolymer is washed once with fresh methanol and then 1.5 liters of cyclohexane are added. The copolymer is stirred at 50°C until it is dissolved in the cyclohexane and the solution is removed from entrained water and methanol by aerotropic distillation. Gravimetric determination of the solids content of the cyclohexane copolymer solution gives a polymer content of 29 grams. NMR analysis of the composition shows that the copolymer contains 79.6 mole percent 1,3-butadiene.

Example 18 Hydrogenation of a 1,3-butadiene/ethyl acrylate copolymer.

The 1,3-butadiene/ethyl acrylate copolymer prepared according to Example 17 is hydrogenated according to the procedure of Example 8. Catalyst residues are removed by extraction with 20% aqueous citric acid. Both IR and NMR spectra of the final hydrogenated copolymer show the absence of unsaturation. GPC determination of the molecular weight (calibration with polymethyl methacrylate) gives a w = 6.5 x 10⁵, n = 1.8 x 10⁵ and a w/ n = 3.56. The Performance of the hydrogenated copolymer as a VI improver is illustrated in Table II. This hydrogenated 1,3-butadiene/ethyl acrylate copolymer exhibits high VIes comparable to the hydrogenated 1,3-butadiene/methyl methacrylate copolymer of Example 11 at the same use level in base oil.

Example 19 Preparation of a 1,3-butadiene/butyl acrylate emulsion copolymer.

A 1,3-butadiene/butyl acrylate copolymer is prepared according to the procedure of Example 17, using the same amount of butyl acrylate as ethyl acrylate. The copolymer yield is 41 grams and it contains 84.6 mole percent 1,3-butadiene as determined by NMR.

Example 20 Hydrogenation of a 1,3-butadiene/butyl acrylate copolymer

The 1,3-butadiene/butyl acrylate copolymer prepared according to Example 19 is hydrogenated and isolated according to Example 18 except that 1 ml of 30% aqueous hydrogen peroxide is added to the aqueous citric acid solution to speed up the isolation. Both IR and NMR spectra of the final copolymer show no olefinic absorptions (no unsaturation). GPC gives a w = 9.3 x 105, n = 1.6 x 105 and a w/n = 5.7 (relative to polymethyl methacrylate). The performance of this copolymer as a VI improver is illustrated in Table II. The hydrogenated 1,3-butadiene/butyl acrylate copolymer exhibited high VIe, comparable to the 1,3-butadiene/ethyl acrylate copolymer of Example 18 and the 1,3-butadiene/methyl methacrylate copolymer of Example 11 at a slightly lower use level in the base oil.

Example 21 Preparation of an isoprene/methyl methacrylate emulsion copolymer

An isoprene/methyl methacrylate copolymer is prepared according to Example 17 except that the polymerization temperature is maintained between 25-28°C by cooling with ice water. The amounts of reactants are as follows: 50 grams of isoprene, 28 grams of methyl methacrylate, 0.16 grams of n-dodecyl mercaptan, 0.16 grams of cumene hydroperoxide, 150 ml of deionized water, 0.30 grams of ferrous sulfate neptahydrate, 0.28 grams of tetrasodium pyrophosphate, 0.78 grams of sodium lauryl sulfate, and 2.43 grams of Triton X405 (70% aqueous). 12 grams of the copolymer are recovered and the NMR spectrum of the copolymer shows that the copolymer contains 66.7 mole percent isoprene.

Example 22 Hydrogenation of an isoprene/methyl methacrylate copolymer

The isoprene/methyl methacrylate copolymer of Example 21 is hydrogenated and the catalyst residues are removed according to the procedure of Example 20. The copolymer requires twice the amount of catalyst and allowed to react twice as long as in Example 20; however, the final copolymer exhibits some unsaturation by IR and NMR. Integration of the NMR spectrum shows that about 35% of the isoprene double bonds are retained. The performance of this copolymer as a VI improver is illustrated in Table II. Although the use level of this copolymer base oil is higher than the butadiene/methyl methacrylate, /ethyl or /butyl acrylate copolymers, the VIe was much higher due to a lower viscosity at 37.8°C (100°F).

Example 23 Preparation of a 1,3-butadiene/methyl methacrylate/cetyl eicosyl methacrylate/dodecyl pentadecyl methacrylate emulsion copolymer

883.4 ml of deionized water, 4.62 grams of sodium lauryl sulfate, 12.20 grams of Triton N-100 (an ethoxylated dodecylphenol in which the number of ethylene oxide units is 9.5 on average), 1.71 grams of tetrasodium pyrophosphate, 1.79 grams of ferrous sulfate heptahydrate, 105 grams of cetyl eicosyl methacrylate, 165 grams of dodecyl pentadecyl methacrylate and 92 grams of 1,3-butadiene are charged to a 2 liter Parr reactor. The mixture is maintained at a temperature of 28-36ºC, and 30 grams of methyl methacrylate containing 1.00 grams of cumene hydroperoxide dissolved therein is continuously fed into the constantly stirred reactor over a period of 3 hours. At the end of the addition of the methyl methacrylate and catalyst, the reaction mixture is stirred for 5 hours. Then the reaction contents are emptied into 2 liters of methanol containing 1.10 grams of hydroquinone to precipitate the copolymer. The precipitated copolymer is washed with 2 liters of fresh methanol and then dissolved in 2 liters of cyclohexanone. Water and methanol are removed by azeotropic distillation to a volume of about 1.5 liters (1,200 grams). The solids content of the copolymer in the cyclohexane is 5.5%, representing a copolymer yield of 66 grams.

Example 24 Hydrogenation of a 1,3-butadiene/methyl methacrylate/higher alkyl methacrylate copolymer

The copolymer of Example 23 is hydrogenated as in Example 15, but with twice the amount of catalyst. The IR of the hydrogenated copolymer suggests that some trans double bonds may remain after removal of residual catalyst, but the NMR spectrum shows no olefinic protons. This indicates that at least 95% of the unsaturation is reduced. The ASTM pour points of blends formulated with this hydrogenated pour point VI improver are shown in Table III, while the VI properties are illustrated in Table II.

Example 25 Preparation of a dispersing, pour point reducing VI improver

60.7 grams of a solution of the hydrogenated 1,3-butadiene/methyl methacrylate/higher alkyl methacrylate copolymer of Example 24 in a solvent of higher alkyl isobutyrates obtained from from the hydrogenation of the higher alkyl methacrylates, where the solution contains about 50% solids, is added to a three-necked round bottom flask equipped with a mechanical stirrer, nitrogen inlet port, and thermometer. The polymer solution is heated to 110°C and 4.55 grams of N-vinylpyrrolidinone (NVP) (15 wt.% polymer) grafting monomer is added. The solution is stirred at 110°C for 15 minutes and 0.72 grams of 85% t-butyl perbenzoate (0.2% based on polymer substrate) (in mixed xylenes) is added to the polymer solution. The solution is stirred at 110°C for 0.5 hour. The reaction temperature is then raised to 140°C at 10°C intervals over 0.5 hours and held at that temperature for one hour to complete the graft polymerization reaction. The reaction mixture is then heated to 155°C at 0.5 mm pressure to distill off volatiles and diluted with N-Oil 100. Gel visible in the oil is removed by filtration. The graft polymer solution, which contained 11.7% solids, was tested for asphaltene dispersibility and found to have a rating of 4P. The performance of the graft polymer as a VI improver is illustrated in Table II and as a pour point depressant in Table III.

Example 26 Preparation of a dispersing, pour point reducing VI improver

10.87 grams of the hydrogenated copolymer of Example 24 isolated from the cyclohexane hydrogenation solvent is precipitated in methanol and added to a 250 mL three-necked round bottom flask equipped with a mechanical stirrer, thermometer and nitrogen inlet port. 29.3 grams of the pale neutral oil is added to the hydrogenated copolymer. The reaction flask is thoroughly purged with nitrogen and the solution is stirred at 120°C for about 4 hours until the polymer dissolves. 0.82 grams of the N-vinylpyrrolidinone (7.5 wt.% polymer) graft monomer is added to the reaction flask. After 15 minutes of stirring, 0.25 grams of 85% t-butyl perbenzoate initiator in mixed xylenes is added to the flask. The temperature is held at 120ºC for 0.5 hours and then raised to 140ºC at 15 minute intervals. The temperature is held at 140ºC for 1 hour to complete the graft polymerization reaction. Additional N-Oil 100 is added and the volatiles are removed by stripping to a temperature of 155ºC at a pressure of 0.5 mm. The hot oil polymer solution is filtered through cheesecloth to remove gel particles and results in a 5.0% polymer solution in oil. The graft copolymer is an IP asphaltene dispersant. Its VI improving properties are shown in Table II and its stick point depressing properties in Table III.

Example 27 Preparation of a 1,3-butadiene/higher alkyl methacrylate emulsion copolymer

The procedure of Example 1 is repeated to prepare 43 grams of copolymer from a monomer mixture containing 100 grams of 1,3-butadiene, 210 grams of dodecyl pentadecyl methacrylate, Contains 70 grams of cetyl eicosyl methacrylate and 1.00 grams of cumene hydroperoxide. All other reagent amounts are described in Example 1.

The copolymer contains 87 mole percent butadiene.

Example 28 Hydrogenation of the copolymer of Example 27

The copolymer of Example 27 is hydrogenated in cyclohexane according to the procedure of Example 8. The IR spectrum suggests some saturation but the NMR spectrum shows no olefinic absorptions, indicating that at least 95% of the double bonds have been hydrogenated. The properties of the hydrogenated copolymer as a VI improver and as a pour point depressant are illustrated in Tables II and III, respectively.

Example 29 Preparation of a dispersing, pour point reducing VI improver

10.73 grams of the hydrogenated copolymer in a solution of 33 grams of N-Oil 100 and 11.3 grams of mixed higher alkyl butyrates are graft polymerized with 1.65 grams of N-vinylpyrrolidinone according to the procedure of Example 25. Very little gel is formed. The product is an IP asphaltene dispersant. The graft copolymer contains 0.10% N. The VI properties and pour point depressability are illustrated in Table III.

Example 30 Preparation of a dispersing VI improver

A solution of 19.0 grams of a hydrogenated butadiene/methyl methacrylate copolymer prepared according to Example 1 in 31.0 grams of N-Oil 100 (38% solids) is placed in a glass reactor, purged with nitrogen and heated to 110°C. 1.43 grams of N-vinylpyrrolidinone (7.5% based on polymer solids) is added to the copolymer solution and the solution is stirred for 15 minutes. The temperature is then raised to 140°C over a period of 30 minutes and held at 140°C for one hour. The solution is stripped at 0.5 mm pressure and at 145°C while additional N-Oil 100 is added. The final product is a 11.5% solution of a V1 dispersant improver in N-Oil 100, giving a dispersibility rating of 6P. Column chromatography shows that 79% of the polymer has been grafted. Microanalysis of the solid polymer gives %Nk = 0.89, which corresponds to an average N-vinylpyrrolidinone content of 7.1%.

The following tables illustrate the VI improvement, shear stability, oxidative and thermal stability, BPT, pour point depressability and dispersibility of the copolymers of this invention. TABLE I Example Chain Transfer Agent Wt.%, on Total Monomers Copolymer Yield (grams) Recovery Method Mole % 1,3-butadiene in Copolymer¹ Extraction³ Precipitation

¹ By NMR (mol% 1,3-butadiene in the feed was 77%)

² Reference: Polymethyl methacrylate

³ Toluene extraction and hydrogenation solvent

&sup4; Contains gel; yield of soluble polymer not determined

5 Hydrogenated copolymer had a w = 2.2 x 105, n = 8.8 x 104, and w/ n = 2.5

Table I presents a summary of the results of Examples 2-8. Examples 2-5 show that as the concentration of the chain transfer agent increases, the molecular weight distribution tends to become narrower. Examples 6 and 7 show that N-Oil 100 is not a very active chain transfer agent and that the weight average molecular weight of the copolymer and the w/n are significantly higher than when n-dodecyl mercaptan is used as a chain transfer agent.

Precipitation is preferred over extraction because it allows recovery of all of the copolymer, whereas extraction allows recovery of only about 50 to 70% of the copolymer. The butadiene concentration in the copolymer is very close to the concentration of butadiene in the feed, indicating very little concentration drift.

Table II illustrates the VIe and %SLDTP of the copolymers of Examples 9-16, 18, 20, 22, 24-26, 28 and 29 compared to base oil. The highest VIe is achieved with the isoprene/MMA copolymer of Example 22; however, the use level and %SLDTP are higher than with Bd/MMA (Example 11). The most shear stable copolymer is Example 16, while Example 18 is the least shear stable. TABLE II Example Base Oil % Polymer 5' Sound % SLDTP Viscosity CST at ºC ( ºF) Base Oil¹ Isoprene/MMA Graft Copolymer Graft-Bd/HAM none

¹ Base oil contains 4.0% ashless dispersant, 8.2% detergent/inhibitor pack, 60-87% Neutral Oil 150, and the balance Neutral Oil 100.

² HAM = Higher Allyl Methacrylate.

Table III illustrates the pour point depressing ability of the copolymers of Examples 24, 25, 26, 28 and 29. All of these copolymers exhibit a pour point reduction over base oil of at least 5.6°C (10°F) and can result in a reduction as high as 13.9°C (25°F). TABLE III Pour Point Depressant Fluids of Hydrogenated Copolymers EXAMPLE % POLYMER VISCOSITY, CST Pour Point Base Oil¹ none

¹ Base oil contains 4.0% ashless dispersant, 8.2% detergent/inhibitor pack, 60-87% Neutral Oil 150, and the balance Neutral Oil 100.

Table IV compares the viscometric properties of the hydrogenated butadiene/methyl methacrylate copolymers of this invention with other conventional VI improvers. The copolymers of this invention have VIes comparable to conventional VI improvers at use levels ranging from 35-45% lower than polymethacrylates and up to about 10% higher than dispersant ethylene/propylene copolymers. The BPTs of the copolymers of this invention are equivalent to polymethacrylates and better than the BPTs of the ethylene/propylene and dispersant ethylene/propylene copolymers. In addition, the VIes are much higher than the VIes of the British Patent '749 copolymers at lower use levels (Example 1, homogenized, 4 passes). In addition, the shear stability of Bd/MMA copolymers is superior to commercially available ethylene/propylene copolymers and equivalent or better than polymethacrylates. TABLE IV Comparison of Viscometric Properties of Hydrogenated Butadiene/Methyl Methacrylate Copolymers with Other VI Improvers¹ Viscosity, CST Polymer Type % Polymer Polymethacrylate Hydr. Styrene/Isoprene Ethylene/Propylene Dispersant, EP⁵ Example

¹ Base oil formulation contains 4.0% ashless dispersant, 8.2% detergent/inhibitor pack, and a blend of Neutral Oil 150 and 100 to give a Cold Crank Simulator (C.C.S.) (ASTM D- 2602) (Low Temperature High Shear Viscosity) viscosity less than 3.5 Pa.s (35 poise) at -20ºC for a full formulation (SAE J-300 Sept. '80).

² Homogenized, 4 passes at 552.6 bar (8000 psig)

³ Homogenized, 8 passes at 552.6 bar (8000 psig)

&sup4; NP = Not reported

&sup5; Dispersant ethylene/propylene copolymer

Table V shows the thermal stability of various VI improvers. The copolymers of this invention are more thermally stable in air than the conventional VI improvers and are generally more stable in nitrogen than the commercial VI improvers except hydrogenated styrene/isoprene at T50. TABLE V TGA data of various VI improvers Polymer Air

¹ Ethylene Propylene, sold by B. F. Goodrich as Epcar 506 ("Epcar" is a trade name)

² Hydrogenated styrene-isoprene sold by Shell Company as Shellvis 40 ("Shellvis" is a trade name)

³ Homogenized, 4 passes

&sup4; Homogenized, 8 passes

⁵ T₁₀₋, T₂₀₋ and T₅₀₋ are temperatures, ºC, at which 10, 20 and 50% of the polymer has volatilized or been lost, measured by weight reduction of the test sample. The heating rate used in the thermogravimetric test was 20ºC/minute.

Claims (9)

1. Graft copolymer characterized in that it comprises a copolymer substrate and a polar nitrogen-containing graft monomer polymerized onto the substrate, and wherein the copolymer substrate: (I) the polymerized product of (a) a conjugated diolefin having 6 carbon atoms or less per molecule and (b) a lower alkyl acrylate or lower alkyl methacrylate in which the alkyl group contains 8 carbon atoms or less per molecule; (II) has a weight average molecular weight of 60,000 to 1.6 x 10&sup6; and (III) is hydrogenated so that no more than 5% residual unsaturation, determined by spectroscopy, is present. 2. A graft copolymer as claimed in claim 1 which contains from 0.2 to 1.0 percent nitrogen and from 0.05 to 0.5 weight percent homopolymerized graft monomer. 3. A graft copolymer as claimed in claim 1 or claim 2, wherein the copolymer substrate comprises 1,3-butadiene and methyl methacrylate, and the polar nitrogen-containing graft monomer comprises one or more of N-vinylpyrrolidinone, 2-vinylpyridine and 4-vinylpyridine. 4. A graft copolymer as claimed in any preceding claim, wherein the copolymer substrate comprises the polymerized product of (a) a conjugated diolefin having 6 carbon atoms or less per molecule, (b) a lower alkyl acrylate or lower alkyl methacrylate in which the alkyl group contains 8 carbon atoms or less per molecule, and (c) one or more higher alkyl methacrylates in which the alkyl groups contain 12 to 20 carbon atoms. 5. Process for the preparation of a hydrogenated copolymer, characterized in that it comprises : (I) emulsion copolymerizing (a) a conjugated diolefin having 6 carbon atoms or less per molecule with (b) a lower alkyl acrylate or lower alkyl methacrylate in which the alkyl group contains 8 carbon atoms or less per molecule, optionally together with (c) one or more higher alkyl methacrylates in which the alkyl groups contain 12 to 20 carbon atoms, in an aqueous surfactant solution in the presence of a catalyst at a polymerization temperature of 5 to 40°C to form a copolymer; (II) catalytically hydrogenating the copolymer in the presence of a hydrogenation catalyst at a pressure of 7.91 bar to 35.09 bar (100 to 500 psig) to reduce substantially any diolefin unsaturation of the copolymer so that there is no more than 5% residual unsaturation as determined by spectroscopy; (III) if necessary, degrading the copolymer before or after the hydrogenation step (II) so that the copolymer has a weight average molecular weight of 60,000 to 1.6 x 10⁶; and (IV) Graft polymerizing the polar nitrogen-containing monomer onto the hydrogenated copolymer. 6. A process as claimed in claim 5 in which from 0.5 to 8 weight percent of a polar nitrogen-containing grafting monomer, based on the weight of the copolymer substrate, is used in the graft polymerization. 7. An oil composition comprising (i) a lubricating oil and (ii) a dispersing and viscosity index improving amount of a graft copolymer as claimed in any one of claims 1 to 3. 8. An oil composition comprising (i) a lubricating oil and (ii) a dispersant, a pour point depressant and viscosity index improving amount of a graft copolymer as claimed in claim 4. 9. A fuel composition comprising (i) a hydrocarbon fuel and (ii) a dispersive amount of a graft copolymer as claimed in any one of claims 1 to 3.